This invention relates to a method and a facility for the treatment of animal waste from a plurality of concentrated animal feed operations.
Concentrated Animal Feed Operations (CAFOs), for example, dairy farms, are recognized as a major source of water pollution world wide. The volume of waste matter produced by these operations is significant. Even a modestly sized agricultural community having about 25,000 head of dairy animals distributed over a number of individual operations produces on the order of 200 tons of liquid manure per day. The manure from these operations contains high concentrations of nitrogen and phosphorous. When released into the environment, these nutrient pollutants cause algal blooming in lakes and rivers and contaminate groundwater with nitrates, rendering the water unfit for human consumption.
CAFOs have limited options for disposing of the manure. Because CAFOs typically operate at low profit margins, the most common method of manure disposal is also the least expensive method, namely, the discharge of untreated manure onto farm fields where a portion of the nutrients may be treated by bacteria in the soil or taken up by plants. However, there are limits to the amount of manure and the rate at which the manure can be processed by this method. Large amounts of pollutants from untreated manure are washed off the fields by rain water where they infiltrate through the ground into the groundwater as well as enter streams, lakes and rivers of the surrounding watershed.
Another option is the anaerobic digestion of manure on site at each operation. Although costly in terms of capital expenditure and operational requirements, this method provides for the production of heat and electricity for use by the farm as compensation. However, the anaerobic digestion process yields water soluble nutrients (nitrogen and phosphorous) as a waste product. This waste product is discharged onto the farm fields. Being water soluble, the pollutants are readily dissolved and carried away in water runoff or infiltrate into the groundwater before they can be treated by bacteria or plants. This results in even higher concentrations of pollutants entering the groundwater and the watershed more rapidly than if untreated manure were applied.
There is clearly a need for a method and a facility for treating animal waste for CAFOs that is both economically viable and effective at reducing or eliminating the pollutants released into the environment.